The virtual machines (also referred to as VMs) are run, by a virtualization technology, on a physical computer logically divided into a plurality of computers (VMs) each executing an operating system (referred to as a guest OS) independent from others. The integration and consolidation of the operating systems (OSs) implemented in a plurality of computers to one computer allows an effective use of hardware resources such as a central processing unit (CPU) and a storage and may save power and spaces. Since the Kyoto Protocol came into effect in 2005, the environmental efforts of companies and local governments to address the global warming issue have received attention, and the needs for power saving with server virtualization have increased.
Power saving operation methods have been known by which virtual machines are efficiently integrated in accordance with work loads to shut down power supply to redundant servers, by using a live migration technology that moves a virtual machine in operation to another server without stopping. “VMware (registered trade mark) VirtualCenter” by VMware, Inc. is known as one of management tools that automatically implement the live migration in accordance with a load status of each virtual machine.
Alternatively, a method that implements the live migration on the basis of the energy consumption and resource utilization in the server running virtual machines has been proposed (for example, refer to Japanese Laid-open Patent Publication No. 2007-536657).
The methods for resource allocation on a server may include a method that monitors the load statuses of virtual machines and changes the resource allocation, a method that changes the resource allocation to a guest OS in accordance with a energy consumption control request issued by the guest OS, and a method that controls unused system resources to save power.
Conventional technologies monitor the statuses of virtual machines and change the resource quota to a virtual machine with a low load or release unused resources.